Density Functional Tight-Binding Model for Lithium–Silicon Alloys

Abstract

The predictive power of molecular dynamic simulations is mainly restricted by the time scale and model accuracy. Many systems of current relevance are of such complexity that they require addressing both issues simultaneously. This is the case of silicon electrodes in Li-ion batteries, where different Li x Si alloys are formed during charge/discharge cycles. While first-principles treatments for this system are seriously limited by the computational cost of exploring its large conformational space, classical force fields are not transferable enough to represent it accurately. Density Functional Tight Binding (DFTB) is an intermediate complexity approach capable of capturing the electronic nature of different environments with a relatively low computational cost. In this work, we present a new set of DFTB parameters suited to model amorphous Li x Si alloys. Li x Si is the usual finding upon cycling the Si electrodes in the presence of Li ions. The model parameters are constructed with a particular emphasis on their transferability for the entire Li x Si composition range. This is achieved by introducing a new optimization procedure that weights stoichiometries differently to improve the prediction of their formation energies. The resulting model is shown to be robust for predicting crystal and amorphous structures for the different compositions, giving excellent agreement with DFT calculations and outperforming state-of-the-art ReaxFF potentials.

Diversity of Behavior after Collisions of Sn and Si Nanoparticles Found Using a New Density Functional Tight-Binding Method

“…To complete the model, the V rep (eq ) parameters are optimized using the ”Milonga” algorithm presented in our recent article, which uses the TANGO code with the aim of predicting relative formation energies of different compositions. As we did in our previous work, we build the training data set using compressions and expansions of the bulk structures of pure Si (mp-149), Sn (mp-117), and the metastable SiSn (mp-1009813) .…”

“…The resulting band structures of Sn are shown in Figure S1 of the Supporting Information. Note that, for the case of Si, we use the same parameters as in our previous work, 64 and the corresponding band structures can be seen in Figure S1 of that reference.…”

“…In our previous DFTB parametrization of the Si−Li system, 64 we introduce a new electronic structure optimization procedure that weights the chemical structures differently to improve the prediction of their formation energies. The model resulting from the application of this new protocol proved to be robust in predicting crystalline and amorphous structures for the entire range of Si−Li compositions, showing excellent agreement with DFT calculations and exceeding the state-ofthe-art ReaxFF potentials.…”